Federal records show that Michael and Donna Nicholson, parents of the candidate, both gave the maximum $2,700 donation in December to Sen. Tammy Baldwin, the Wisconsin Democrat Nicholson hopes to unseat later this year.

"My parents have a different worldview than I do, and it is not surprising that they would support a candidate like Tammy Baldwin who shares their perspective," Nicholson said in a statement. CNN was the first to report the donations.

Nicholson, a businessman and U.S. Marine veteran, is squaring off against state Sen. Leah Vukmir in the state GOP primary in August.

Donna Nicholson has been a longtime Democratic financial supporter, having previously given $441 to Baldwin and another $500 to former Sen. Russ Feingold of Wisconsin. She chipped in $500 to Democratic presidential nominee Hillary Clinton.

More recently, she has written checks to such Democratic candidates as Rep. Mark Pocan of Wisconsin and former Sen. Al Franken of Minnesota and Sen. Tim Kaine of Virginia.

Nicholson's mother is also a frequent donor to Democracy for America, a liberal political action committee that has endorsed Randy Bryce, a Democrat hoping to challenge House Speaker Paul Ryan, a Wisconsin Republican.

Nicholson's parents can each give another $2,700 to Baldwin for the general election.

"I'm a conservative today not because I was born one, but because of the experience I earned as a Marine in combat, my experience as a husband and father, my choice to be a Christian, the schools I chose to attend and the decision to pursue the career that I have," Nicholson said in his statement on Tuesday.

"Regardless of who may disagree with my life decisions, I would not trade these experiences for anything, and they will always guide my views as Wisconsin's next U.S. senator."

The tension between Nicholson and his parents is nothing new.

In 2000, when Nicholson was the president of the College Democrats of America, he told the Journal Sentinel that his parents might not like it if he ran for office in Wisconsin.

"They're afraid of being found out as the only Democrats in Mequon," Nicholson said on Aug. 14, 2000.

Nicholson has acknowledged his past ties to the Democratic Party. There has been some dispute over when he changed political parties; he has said it was a gradual shift.